While you cannot customize the default welcome mail for Office 365 Groups, disabling the welcome mail is possible with an extra parameter in the Set-UnifiedGroup cmdlet in Exchange PowerShell: -UnifiedGroupWelcomeMessageEnabled:$false. See https://docs.microsoft.com/en-us/powershell/module/exchange/users-and-groups/set-unifiedgroup
Use this as a part of a custom group creation flow if you would like to restrict and/or customize the welcome mail for many groups across your tenant.Ben K. supported this idea ·Ben K. commented
the problem with this comlet is, if you run get-unifiedgroup before and after making the param returns null. no confirmation it's set or not. and, some instances the welcome message still sent.
please note when creating a unified group it takes sometimes to be able to get the group and set it. what's is the time frame sending out welcome message?
12 votesBen K. commented
this is also posting a big concern to use Office Group as an admin. as you may imagine there is reason admin (owner) should not be a group member, but in Stream even Stream admins can't see those groups if they are not owner.